This invention relates to apparatus for treating liquids and more particularly to apparatus that employs sedimentation to remove unwanted materials from water.
In sedimentation apparatus having a plurality of liquid treatment zones, optimum treatment results can be attained when flow of solids between such zones is controllable over a wide range of operating conditions. Such apparatus may have a solids settling zone, a solids mixing and recirculation zone and a solids uptake zone. The bottom of the uptake zone communicates with the settling zone and the upper end of the uptake zone communicates with the mixing and recirculation zone. The lower portion of the mixing and recirculation zone communicates with the settling zone. Solids from the settling zone and treatment chemicals are mixed with incoming untreated liquid in the uptake zone. This can be achived by flowing the incoming liquid and treatment chemicals into the uptake zone through nozzles which cause a turbulent updraft that draws in settled solids.
The quantity of solids recirculating in such apparatus should be maintained in an optimum range to insure ample solids to achieve coagulation and clarification, while preventing solids from being discharged with the treated liquid. When the volume of liquid flowing through the apparatus changes, the quantity of solids being recirculated will also change. Prior arrangements used to adjust the recirculation of solids to compensate for changes in liquid flow have had a limited flow control range in the order of two to one or less.